Voice-controlled circuits



Dec. 9, 1930. A. CARPE v1,784,178

VOICE CONTROLLED CIRCUITS f,

Filed Aug. 18, 192s Energy E'eyl/elg 27. 4 INVENToR ClU/yne BY Wg ATTORNEY Patented Dec. 9, 1930 UNITED STATES PATENT OFFICE v ALLEN omnes NEW Yonx, N. Y., AssIGNoa To AMERICAN TELEPHONE AND TELE- k GRAPH COMPANY, A CORPORATION F NEW YORK voren-CONTROLE cmcu-rrs' Application led August 18, 1928. Serial No; 300,478.

i This invention relates to voice operated devices in which a. speech wave is utilized to control the transmission through or operation of a signal circuit. y

While the invention is of general appllcation, it is illustrated in connection with an amplifier in which the output circuit is con-V nected back to the input circuit through a control element for the purpose of renderlng the amplifier inoperative unless the input energy exceeds a certain threshold value. It is Well known that the energy of speech waves varies widely with frequency, the lower frequencies of the voice range, and particularly the vowel '.1 sounds, being of relatively largerenergy,

while the higher frequencies, which are more characteristic of consonant sounds, are of relatively `small energy. The threshold value of the control circuit must, therefore, be low enough to enable the system to respond to the higher frequency components of small energy. .y

lVhere the circuit is subject to cross-talk, however, the lower frequencies involved in 'f5 the cross-talk wave may have sufiicient` energy to exceed the threshold value so that a false o eration of the control circuit would result. 'lo avoid this it is proposed, in accordance with the presentv invention, to render the control circuit less responsive at those-frequencies whose energy is-large than to frequencies whose energy is small.` This permits making the threshold value of the control cir-` cuit low enough to permit response to the low energy frequencies without responding to the cross-talk frequencies of large energyfthe cross-talk frequencies of large energy being ineii'ective by reason of having been reduced or attenuated in the control circuit before being applied to the sensitive control element.

Due to the fact that the-'frequencies of theV voice band which are of the largest energy occur in the lower part of the range, it is desirable in some instances to completely suppress these frequencies from the control Vcircuit by suitable selecting means,rin which event the threshold value to which the control element responds may be reduced to a point ust above the energy level of the highrectifying element only will be su er frequencies encountered in' thecross-talk embodying the invention while Figs. 6, 7 and 8 illustrate various equalizing devices to be used inconnection with the control circuit.

As illustrated in Fig. 5, vthe transmission circuit L has included therein a vacuum tube amplifier A. In order that the amplifier may be inoperative unless the input energy eX- ceeds a certain threshold value, the output or plate circuit of the amplifier is connected to the input or grid circuit through a control circuit which fmay,if desired include elements s u'ch'as rectifying, amplifying and=current hmiting devices. For practical urposes a cient, and this element is represented symbolically by the rectifier D. Thegrid circuit is biased by means of a` battery C to such a negative value that normally substantially no plate current can flow, and hence the amplifier ispractically inoperative under these conditions. When a voice wave is applied, however, some of the voice energ from the out ut'of the ampli- Iier is recti ed by the rectidjer D and applied to the grid of the am lier across the terminals of a condenser i? in such a direction as to oppose the potential from'the battery C. In the case of Va voice wave' producing a rectiied 4 will be rendered suiciently less negative so that it becomesan eiiicient ampliier. Y

As has been previously stated, it is well known that the energy of a speech wave `varies wldely with frequency, the lower frequencies which arekmost prominentin vowel sounds being of large energy compared with' the hlgher frequencies which are characteristic of consonant sounds. If, therefore,in Fig. 5, the control circuit picks off from the output of the amplifier a fractionV ofi-the energy of a train of speech waves with equal eliciency at all frequencies, it is obvious that the control circuit must be made suiciently sensitive tocurrent of sufficient amplitude the gridV operate on the weakestimportant portions of the controlling signal. In other words, its threshold of operation must be sufficiently low so that the system will respond to the high frequency components of small energy. Under these conditions, however, the control circuit will be much more sensitive than would be necessary to obtain adequate response to those portions of the signal wave which embody different frequencies havingv greater energy. Y v

Furthermore, in order that the circuit may be immune from false operation due to interference and cross-talk, it is clear that the threshold of operation of the control circuit (which is fixed by theweakest portions of the controlling wave) must b egreater than those components of crosstalk or interference which are of largest energy. Now,'while the energy represented by ythe interference mayV actually be very much smaller at a given frequency than. the energy available in the controlling wave at the same frequency, the threshold of the control circuit may be so lowas to renderit liable to interference because this threshold is determined by the energy available in the controlling circuit at some other frequency. This is particularly true where the interference is produced by speech cross-talk because the energy distribution with frequency of the interference would then be approximately the same as that of the controlling speech wave. This is illustrated by the curves of Fig. 1` in which the curve a represents the average distribution of they energy of vocal sounds with frequency, and the curve b represents a corresponding aver age distribution for cross-talk. If the curve c may he` taken as representing the minimum energy necessary to. cause proper response on the part of the amplifier A, or, in other words, if c represents the threshold'of operation, it will beI seen that while this threshold is4 low enough torespond to all portionsl of the speech wave represented by the curve a without responding tothe higher frequency elements of the cross-talk curve b, the lower frequency elements of the cross-talk curve are of sufficient energy to exceed the threshold value and thereby cause falseoperation of the amplifier A. AThis is shown by those por tions of the cross-talk curve between m and u. From these curves of Fig. 1 it is. evident that if we include in the controlcircuit a net-work N so designed as to discriminate against those frequencies which appear in the hump of theV curve a, the amplitude of the components of the cross-talk represented between m and n will also be reduced so that they will fall below the assumed threshold of operation.

The ideal condition would be to have the network N so designed` that voice frequency components applied to vit with varying energies, represented by the curve a, would, after transmission through the network, be

reduced to a common amplitude higher than that represented by the curve c. `While this might be done by designing a suliiciently complicated network N, in practice a sufiicient equalization may be obtained by means of a tuned circuit which is resonant at the peak frequency of the hump of the curve a of Fig. l, and which has suiicient damping so as tc reduce the curve in the vicinity of the peak to approximately the saine level. The network N may, therefore, assume the form illustrated in Fig. 6, in which a tuned circuit comprising inductance L, capacity C and resistance R is shunted across the line conductors so as to attenuate the resonant frequency and the frequencies in the neighborhood of the frequency to which the tuned circuit is resonant. The attenuation of the network N as thus designed may then vary with frequency as represented by the curve Z of Fig. 2, in which case the speech curve represented at L in Fig. l,.after passing through the network N, may assume somewhat the form of the curve represented at a in Fig. 3. Here, it will be observed that the larOe hump in the low frequency range has disappeared, andthe curve representing the energy of speech ei;- hibits only two small humps, with the energy over the entire range departing but little from the average value. All parts of the curve ce, it will be observed, are above curvec representing the threshold of operation. The cross-talk curve will be somewhat as represented at b, ince the cross-talk in the range m, n of l will be attenuated in proportion to the attenuation of normal speech. All parts of the cross-talk wave'b of Fig. 3 are below the threshold of operation of the system, and hence no `false operation will occur in response to cross-talk.

Instead of using a shunt resonant circuit as illustrated in Fig. 6, the network N may comprise an anti-resonant circuit, as illustrated in Fig. C7, in which a loop comprising inductance L and capacity C shunted by resistance It is connected in series with the line conductors. Such a network may have the same attenuation characteristics as illustrated at Z in Fig. 2 so that the system will have the characteristics illustrated by the curves of Fig. 3. y

It willbe noted from the curves a and Z) of Fig. 1 that those speech frequencies whichv cause false operation are the lower frequencies of the voice range represented largely by vowel sounds. It may, therefore, be dc sirable in some instances to actually cause a complete suppression of these lower frequencies inthe control circuit, especially as the funda-mental vowel frequencies are always accompanied by harmonics of smaller energy in the higher portions'ofthe voice range, so that even in the case of pure vowel sounds there will bepsome unsuppressed `frequencies to operate the control circuit. In this case the time constant of the resistance-capacity f the network may assume the form of a filter of the Campbell ty e, for example, a high pass filter such as own in Fig.r8. Such `a filter functions to pass frequencies above a lower limit and to suppress all frequencies below this limit. VThe attenuation curve of the filter of Fig. 8 may assume the form shown at e of Fi 2, in which case the energy of the range of requencies illustrated by the curve a of Fig. 1 Would assume the general form illustrated at a of Fig. 4, after passing through the filter. Consequently, frequencies below the-cut-off frequencyf cannot operate thei system. .They `frequencies above the cut-off point, however, will have energy greater than the threshold value, as will be clear from Fig. 4. The lower-frequencies of the cross-talk will also be suppressed so that the cross-talk curve correspondinlg to b of Fig. 1 will assume the form b Vof ig. 4. This curve, where unsuppressed, is at all points below the threshold value, so that no false operation will occur.

4The use of a filter, with consequent suppression of the lower frequencies as illustrated in the curves of Fig. 4, brings about a further desirable result. as illustrated in Fig. 5, there is a feed-back connection from the output to the input of the amplifier which would cause a singing condition to be set up if the entire loop circuit were responsive to any common freq'uency. To prevent this condition, the control circuit is connected to the input of the amplifier through a combination comprising a capacity X shunted by a resistance r. When energy is applied to the control circuit `from the output oftheV amplifier it must build up in the capacity-resistance combination to a certain minimum value before singing can result. This minimum value must be such that the resultant potential on the grid will cause an amplified wave in the plateV circuit at least equal to the original plate Wave which built up the energy in `the resistance-capacity combination. The resistance-capacity combination should, therefore, have a time constant such as to prevent the building-up of this energy to the minimum value within the time of a cycle of the lowest frequency which is to be transmitted. If the input to the controlcircuit is equally responsive to the entire voicek range, the time constantV of the capacity-resistance combination must be large in order to. prevent singing at the lower frequencies, and hence the action of the control circuit will be sluggish. The neutralizing potential upon the grid is built up as slowly as the wave tending to produce singing. Where, however, the control circuit is made relatively unresponsive to low frequencies, it is possible to decrease combination since the circuit is only responsive to the higher frequencies and the resist- In the circuit ance-capacity combination need be only sufficiently sluggish to prevent singing at such higher frequencies. By rendering the control circuit selective by means of a filter, so that low frequencies do not exceed the threshold value of the control circuit, the distortion of the waves transmitted through the amplifier, resulting Vfrom thev sluggishness of the control action, will be correspondingl reduced.

, It will e obvious that the general principles herein, disclosed may be embodied in many other organizations widely different ,from` those illustrated withoutv departing from thespirit of the invention as defined in the followingclaims. f

VVVhatis claimedis: 1 y

1. `In a transmission system, a transmission element', a voice responsive control circuit for Vdetermining the effectiveness ofsaid ltransmission element in response to voice Vfrequency components of predetermined magnitude, and means associated with said control circuit to discriminate against those frequencies of an applied voice wave which are in a range of large energy, whereby corresponding components of induced cross-talk vwill be reduced to a magnitude smaller than applied voice ,frequencies in a range of small energy.l

2. Ina transmission system, a transmission element, a voice responsivecontrol circuit .for determining the effectiveness of said transmission element in response to voice frequency components of predetermined magnitude, and means associated with said. control circuit to reduce those frequency components of an applied voice wave which are in a range of large energy to a value not greater than that of applied voice frequency components in a range of small energy, whereby relatively large energy components of induced crosstalk will be'reduced to a magnitude smaller than applied voice frequencies of small encomponents as'lie in a-range of large energy,

whereby corresponding frequency components of induced cross-talk will be suppressed.

4. In fa transmission system, a transmission element, a voice responsive control circuit for determining the effectiveness of said transmissison element in response to voice frequency components of predetermined magnitude, means associated with vsaid control circuit to substantially suppress from an transmission system, a transmis-A components as lie in a range of large energy, whereby lcorrresponding frequency components of induced cross-talk will be suppressed, and means for preventing singing of the transmission element and control 'circuit at unsuppressed frequencies.

5. In a transmission system, a transmission element which is normally substantially inoperative to transmit, a voice responsive control circuit for rendering said transmission element operative inresponse to voice frequency components of small energy of predetermined minimum value, and means associated Wit-h said control circuit to discriminate against those frequencies of an applied voice Wave which are in a range of large energy, whereby corresponding components of induced cross-talk will be reduced to a magnitude smaller than applied voice frequencies in a range of small energy.

6. In a transmission system, a transmission element which is normally substantially inoperative to transmit, a voice responsive control circuit for rendering said transmission element operative in response to voice frequency components of small energy of predetermined minimum value, and means associated With said control circuit to reduce those frequency components of an applied voice Wave Which arc in a range of large energyto a value not greater than that of applied voice frequency components in a range of small energy, whereby relatively large energy components of induced crosstalk Will be reduced to a magnitude smaller than applied voice frequencies of small energy.

7. In atransmission system, a transmission element Which is normally substantially inoperative to transmit, a voice responsive control circuit for rendering said transmission element operative in response to voice frequency components of small energy of predetermined minimum value, and means associated with said control circuit to substantially suppress from an applied voice Wave such of its frequency components as lie in a range of large energy, whereby corresponding frequency components of in duc-ed cross-talk will be suppressed.

S. In a transmission system, av transmis mission element which is normally substantially inoperative to transmit, a voice. responsive control circuit for rendering said transmission element operative in response to voice frequency components of small energy of predetermined minimum value, means associated with said control circuit to substantially suppress from an applied voice Wavesuch of its frequency components as lie in a. range of largeenergy, whereby corn responding frequency components of induced cross-talkY Willy be suppressed, and means for preventing singing of the transmission element and control circui-t at un suppressed frequencies.

9. In a transmission system, a transmission circuit including an amplifier normally substantially inoperative to amplify, a voice responsivecontrol circuit including means responsive to applied voice frequency components of small energy greater than a predetermined minimum value to render said amplifier operative 'to amplify efficiently, and means associated with said control circuit to discriminate aga-inst those frequencies of an' applied voice Wave which are in a range of large energy, whereby corresponding components of induced cross-talk Will be reduced toa magnitude smaller than applied voice frequencies in a range of small energy.

l0. In a transmission system, a transmission circuit including an amplifier normally substantially inoperative to amplify, a voice responsive control circuit including' means responsive to applied voice frequency componente of small energy greater than a predetermined minimum value to render said amplifier operative to amplify efficiently, and aie-ans associated vvith said control circuit to reduce frequency components of an applied voice Wave which are in a range of la- 'e energy to a value not greater than that of applied voice frequency components in a range of small energ` whereby relatively large energy components of induced crosstallr iill be reduced to a magnitude smaller than applied voice frequencies of small energy.

ll. In a. transmission system, a. transmission circuit including an amplifier normally substantially inoperative to amplify, a voice responsive control circuit including means responsive to'applied voice frequency components of small energy greater than a predetermined minimum value to render said amplifier operative to amplify efficiently, andL means associated With said control circuit to substantially suppress from an applied voice Wave such of'its frequency components as lie in a range of largeV energy, whereby corresponding frequency components of induced cross-'talk Will -be suppressed.

12. In a transmission system, atransmirsion circ-uit including an amplifier normally substantially.inoperative to amplify, a voice responsive control circuit including means responsive to applied voice frequency components of small energy greater than a. predetermined minimum value to render said amplifier operative to amplify efficiently, means associated with said control circuit to "substantially suppress from an applied voice wave such of its frequency components as lie in arange of large energy, whereby corresponding frequency components of induced cross-tallr Will be suppressed, and means for preventing singing of the amplier over the control circuit at unsuppressed frequencies.-

llO

13. In a transmission system, a transmission circuit including a vacuum tube having its grid normally biased to'opera-te on an ineffective part of its characteristic curve, a voice responsive control circuit, means in said control circuit responsive to applied voice frequencies of small energy but greater than a predetermined minimum value to produce a rectified potential, means to apply said potential to the grid of said vacuum tube in such direction as to shift the operation to an effective part of the characteristic of the tube, and means associated with said control circuit to discriminate against those frequencies of an applied voice Wave which are in a range of large energy, whereby corresponding components of induced cross-talk will be reduced to a magnitude smaller than applied voicefrequencies in a range of small energy. l

14. In a transmission system, a transmission circuit including a vacuum tube having its grid normally biased to operate on an ineffective part of its characteristic curve, a

voice responsive control circuit,y means in control circuit responsive to applied voice frequencies of small energy but greater than a predetermined minimum value to produce a rectified potential, means to apply said potential to the grid of said vacuum tube in such direction as to shift the operation to an effective part of the characteristic of the tube, means associated with said control circuit to substantially suppress from an applied voice wave such of its frequency components as lie in a range of large energy, whereby corresponding frequency components of induced cross-talk will be suppressed, and means to prevent singing of the vacuum tube over said control circuit at unsuppressed frequencies. y v

In testimony whereof, I have signed my name to this specification this 17thl day of August, .1928.

v ALLEN CARPE.

said control circuit responsive to applied voice frequencies of small energy but greater than a predetermined minimum value to produce a rectified potential, means to apply said potential to the grid of said vacuum tube in such direction as to `shift the operation to an effective part of the characteristic of the tube, and means associated with said control circuit to reduce those frequency components of an applied voice wave which are 1n a range of large energy to a value not greater than that of applied voice frequency components in a range of small energy, whereby relatively large energy component-s of induced cross-talk will be reduced to a magnitude smaller than applied voice frequencies of small energy.

15. In a transmission system, a transmission circuit including a vacuum tube having its grid normally biased to operate on an ineffective part of its characteristic curve, a voice responsive control circuit, means in said control circuit responsive to applied voice frequencies of small energy but greater than a predetermined minimum value to produce a rectified potential, means to apply said potential to the grid of said vacuum tube in such direction as to shift the operation to an effective part of the characteristic of the tube, and means associated with said controlv circuit to substantially suppress from an applied voice wave such of its frequency components as lie in 'a range of large energy, whereb corresponding frequency components o induced cross-talk will be suppressed.

16. In a transmission system, a transmission circuit including a vacuum tube having its id normally biased to operate on an ine ective part of its characteristic curve, a

voice responsive control circuit, means in said 

